Storm water pollution is often conveyed into our environments from various sources such as from storm water entering lakes and rivers. This type of pollution can threaten the stability of our ecosystems, and the water resources that man's society depends on. Storm water pollution is often referred to a non-point source pollution because its source is everywhere that rain falls. However, storm water is often concentrated in storm drain pipes for conveyance which is a convenient point of applied treatment. Sediments are heavier than water and many of the targeted chemical pollutants readily attach to sediments. Storm water pipes are used for sediment transport as well as water. Sediments that are smaller in size have a higher concentration of these chemical pollutants than larger particles.
A storm water treatment system that can capture very fine sediments such as silt and clay will be more effective than a treatment system that is limited to medium and coarse size sediments. In modern day permitting practices of water sheds, requirements for more demanding pollutant removal efficiencies, and technology that increases the efficiency of storm water treatment will more than likely be required and an important part of the solution. Currently, capturing very fine sediment particles is not able to be easily achieved in current storm water treatment systems.
FIG. 1 is an upper perspective view of a conventional baffle box 10. FIG. 2 is another perspective view of the baffle box 10 of FIG. 1 with cut-away face wall. FIG. 3 is a top view of the conventional baffle box 10 of FIGS. 1-2 with water flow lines. FIG. 4 is a side sectional view of the conventional baffle box 10 of FIG. 3 along arrows 4A with flow lines over the baffles and circulating loop currents within the sediment chambers.
Referring to FIGS. 1-4, a conventional baffle box 10 can include an inlet pipe 20 entering into one end of a baffle box case 40, and an outflow pipe 30 exiting out the opposite end of the box case 40. Inside of the case 40 can be one or more baffles 50 that divide up various sediment chambers 60, 70 and 80.
Referring to FIGS. 3-4, water flows into the box 10 in the direction of arrow 90, and circulates in loops 110 inside of first sediment chamber 60, and flows over baffle 50 in the direction of arrow 120 into second chamber 70. The water then circulates again in loops 110 inside of second sediment chamber 70, and over another baffle 50 in the direction of arrow 120 into third sediment chamber 80 where it again circulates in loops 110, and then exits the box 10 through outflow pipe 30 in the direction of arrow 100. From the first sediment chamber 60 to the third sediment chamber 80, a gradual widening of the flow occurs while sediment 130 is at the bottom of box 10 below water level 140
Baffle boxes are treatment structures that can treat the entire flow of a pipe and has the capability to capture particles that are heavier than water such as sediments. Baffle boxes are used to reduce the velocity of the water flow and reduces turbulence to calm the water which is conducive for the settling of suspended particles. Creating calm water and maximizing retention time within the baffle box will increase the removal efficiency. Although there many different configurations of baffle boxes, laboratory and field testing has yielded data that suggests an optimum configuration for a baffle box. A typical well designed conventional baffle box can have the following general characteristics:
1. Three equally size sediment chambers
2. The length of the vault will be approximately twice the width.
3. The inflow pipe, top of baffles and outfall pipe will be at the same elevation.
4. The inflow pipe size will not exceed half the width of the vault.
Referring to FIGS. 1-4, a majority of the captured sediments in a baffle box 10 will be in the first sediment chamber 60. The average sediment size in the second sediment chamber 70 will be smaller than in the first sediment chamber 60, and average sediment size in the third chamber 80 will be smaller than the sediment in the second sediment chamber 70. Smaller particles take longer to settle than larger particles. The greater the flow volume moving through a baffle box 10 the less the removal efficiency because there will greater turbulence and less retention time. During medium and large flows there is significant turbulence within the sediment chambers 60-80, which can prevent sediments from settling and re-suspend sediments that had been captured in a previous rain event. In larger flows rectangular current can form within the sediment chambers 60-80 and possibly flush most of the previously captured sediments out the end of the baffle box 10.
As water flow enters the baffle box 10 through the inflow pipe 20 the water current gradually spreads wide and down into the first chamber 60. As the current impacts against the first baffle 50 the current turns and flows down the face of the baffle 50. When the current reaches the bottom of the sediment chamber it impacts the sediment 130, agitating it, and then turns back toward the inflow flowing across the captured sediments 130 scouring and re-suspending these sediments. When the current reaches the wall just under the inflow it impacts the wall and turns flowing up the wall toward the inflow pipe 20 and carrying with it scoured sediments.
Finally, as the current merges into the inflowing water from the inflow pipe 20, sediments that had been previously settled across the bottom of the sediment chamber 60 are re-suspended into the highly turbulent inflowing water and are flushed further down the length of the baffle box. The sediments may settle again in the second sediment chamber 70 or third sediment chamber 80, or flush completely out the end of the baffle box 10 through the outflow pipe 30. This rectangular current is also present in the second chamber 70 and third chamber 80. However, the first chamber 60 has significantly greater turbulence than the other chambers 70, 80. This process repeats continuously during the rain event and will dramatically reduce the removal efficiency of the baffle box 10. Thus, the need exists for solutions to the above problems with the prior art.